In a typical prior art magnetic disk recording system a slider containing magnetic transducers for reading and writing magnetic transitions is supported by a suspension as it flies above a disk that is being rotated by a spindle motor. The disk includes a plurality of thin films and at least one ferromagnetic thin film in which the recording (write) head records the magnetic transitions in which information is encoded. The magnetic domains in the media on can be written longitudinally or perpendicularly. The read and write head portions of the slider are built-up in layers using thin film processing techniques. Typically the read head is formed first, but the write head can also be fabricated first. The conventional write head is inductive and the read sensor is magnetoresistive. In the typical process of fabricating thin film magnetic transducers, a large number of transducers are formed simultaneously on a wafer. After the basic structures are formed the wafer may be sawed into quadrants, rows or individual transducers. Further processing may occur at any or all of these stages. Although sawing has been the typical method for separating the wafers into individual sliders, recently reactive ion etching (RIE) or deep reactive ion etching (DRIE) with a fluorine containing plasma has been used. The surfaces of the sliders perpendicular to the surface of the wafer that are exposed when the wafers are cut eventually form the air bearing surface (ABS) of the slider.
FIG. 1 is a simplified illustration of a midline section of one type of prior art slider 20 containing magnetic transducers for longitudinal recording. The slider 20 is shown prior to being sawed from the wafer. The components of the read head 22 include the read sensor 35. The write (recording) head 23 includes a coil 33, a pole piece (P1) 45 and a gap layer that forms the write gap at what will become the air-bearing surface (ABS). The zero throat height (ZTH) is defined as the point where the pole piece (P3) 38 first touches the gap layer. The pole pieces are ferromagnetic materials, e.g., NiFe or CoFe. Prior to lapping, the structures that will be at the ABS extend beyond the ABS. As illustrated in FIG. 1 the material to the right of the ABS plane is removed by lapping to achieve precise control of the length of the sensor 35 (which is called the “stripe height”) and the distance from the ZTH to the ABS which is called the “throat height.” The uncertainty of the saw plane would cause unacceptable variations in the stripe height which would lead to unacceptable variations in magnetic performance if not corrected. Lapping is the process used in the prior art to achieve stripe height control in the nanometer range.
After lapping, features typically called “rails” (not shown) are formed on the ABS of magnetic transducer 20. The rails have traditionally been used to determine the aerodynamics of the slider and serve as the contact area should the transducer come in contact with the media either while rotating or when stationary.
Sliders have conventionally been lapped in rows, but it can be advantageous to have the individual sliders cut out prior to lapping. Even though the sliders have been separated, it is possible to lap several at one time by attaching them to carrier.
Current lapping methods are targeted to achieve tight control of the stripe-height. The endpoint of the lapping process is either determined by one or more electro-lapping guides (ELG), which are aligned with the read sensor, or by the sensor resistance itself. Once the ELG value or the read sensor resistance value reach preset target values, the lapping is stopped.
With perpendicular recording heads, critical elements defined by lapping now exist both in the read and write head. Unlike longitudinal head design where the stripe height is the major critical element, perpendicular head design, on the other hand, has several critical structures in both the read and write heads. The current lapping techniques are ineffective for simultaneously defining both read and write elements with tight lapping tolerance.
Much of the prior art on lapping guides is directed toward row lapping. In U.S. Pat. No. 6,027,397 to Church, et al. a row lapping method using two ELGs for simultaneously monitoring the lapping of read write elements is described. The ELG structures and their electrical connections are positioned in the saw kerf regions and not integrated into the slider fabrication process. As critical elements of magnetic heads are scaled downwards tighter dimension control is required. Row lapping is insufficient to achieve the needed lapping tolerances. This can be due to the shape of the slider not being flat. Church, et al., also describe the use of a switch to signify endpoint for throat height lapping control. The switch is closed until lapping reaches the critical point where the switch is opened. This approach can be used with single slider lapping but with a few drawbacks. A subtractive method such as ion milling is the preferred method to fabricate the write pole. If the switch is fabricated simultaneously with the write pole both structures are exposed during ion milling, the physical etching process can cause the structures to shift and distort their alignment. Shadowing effects can also cause problems.